Product Version: Intel(R) Visual Fortran Compiler XE 15.0.0.070
Cause:
The vectorization report generated using Visual Fortran Compiler's optimization and vectorization report options -O2 -Qvec-report2 -Qopt-report:2 states that loop was not vectorized: vectorization possible but seems inefficient.
Example:
An example below will generate the following remark in optimization report:
subroutine foo(a, b, n)
implicit none
integer, intent(in) :: n
real, intent(inout) :: a(n)
real, intent(out) :: b
real :: x = 0
integer :: i
do i=1,n
x = x + a(2*i)
end do
b = x
end subroutine foo
Report from: Vector optimizations [vec]
LOOP BEGIN at f15335.f90(9,5)
remark #15335: loop was not vectorized: vectorization possible but seems inefficient. Use vector always directive or /Qvec-threshold0 to override
LOOP END
Resolution:
Using !DEC$ VECTOR ALWAYS directive in the code will vectorize the loop by overriding efficiency heuristics of the vectorizer.
See also:
VECTOR and NOVECTOR
Vectorization and Optimization Reports
Back to the list of vectorization diagnostics for Intel Fortran